That’s the word here. In a statement on the Kindle Community site, they laid it out.

Dear Customers:

Macmillan, one of the “big six” publishers, has clearly communicated to us that, regardless of our viewpoint, they are committed to switching to an agency model and charging $12.99 to $14.99 for e-book versions of bestsellers and most hardcover releases.

We have expressed our strong disagreement and the seriousness of our disagreement by temporarily ceasing the sale of all Macmillan titles. We want you to know that ultimately, however, we will have to capitulate and accept Macmillan’s terms because Macmillan has a monopoly over their own titles, and we will want to offer them to you even at prices we believe are needlessly high for e-books. Amazon customers will at that point decide for themselves whether they believe it’s reasonable to pay $14.99 for a bestselling e-book. We don’t believe that all of the major publishers will take the same route as Macmillan. And we know for sure that many independent presses and self-published authors will see this as an opportunity to provide attractively priced e-books as an alternative.

Kindle is a business for Amazon, and it is also a mission. We never expected it to be easy!